The present invention relates to a welded flangeless container, and more specifically a steel fuel tank.
The preferred prior art method for manufacturing metal fuel tanks is to lap weld two tank halves along mating circumferential flanges formed into each. This method suffers in that the flanges, which extend outward from the tank, prohibit the tank body from extending to the full expanse of the opening designed to receive it. The circumference of the fuel tank body must be reduced in proportion to the size of the circumferential flange, thereby placing an undesired limit on the volume of the fuel tank.
To overcome this disadvantage, prior artisans have attempted to create a flangeless metal fuel tank. One problem in fabricating a flangeless tank is maintaining the two halves in alignment during welding. The top half wants to drop down "into" or "over" the bottom half-much like a box top on a box. Holding the tops consistently in registration has proven difficult.
A variety of coating materials such as zinc (Zn) are used to protect sheet metal from the hazards of exposure. These coatings generally have a vaporization temperature lower than the temperature necessary to weld the metal. As a result, the coatings vaporize and the resulting gas expands during the welding process. The expanding vapors can be trapped in pockets along the weld line or can blow out through the molten metal thereby creating defects along the weld line. In either case, the strength and leak-tight characteristics of the weld are adversely affected. This problem can be overcome by providing external communication with the weld location through the use of spacers or protrusions stamped along the weld line. The spacers or protrusions maintain a gap between the pieces to be welded and allow the expanding vapors to escape without adversely affecting the weld.
While the use of spacers or protrusions may solve the problem posed by the vaporization of metal coatings, each has shortcomings of its own. Spacers require the additional steps of fabrication and placement. Protrusions, in conjunction with the clamping force, have a tendency to cause the metal to bend or to deform. The clamping pressure causes the metal sheet to pivot at the point of contact between the protrusion and the adjacent metal sheet.